In Release-10 of LTE (Long Term Evolution), CA (Carrier Aggregation) was introduced as control for achieving broadband communications beyond 20 MHz while maintaining “backward compatible”.
The CA is capable of achieving high throughput by performing communications with multiple (a plurality of) CCs (Component Carriers) aggregated.
The CA (“Intra-eNB CA”) in LTE Release-10, however, has a constraint in which CCs that can be aggregated should be under the same radio base station eNB as illustrated in FIG. 4.
For this reason, when a telecommunication carrier desires to implement the CA, the telecommunication carrier is always required to make network deployment such that CCs can be located under the same radio base station eNB. This poses a problem of making flexible network deployment difficult.
In order to solve this problem, as one of techniques for “SCE (Small Cell Enhancement)” in LTE Release-12 and beyond, “Inter-eNB CA” has been studied with the view of introduction. The “Inter-eNB CA” is CA performed with CCs under different radio base stations eNBs aggregated as illustrated in FIG. 5.
As illustrated in a part (a) in FIG. 6, the existing “Intra-eNB CA” is configured such that a single radio base station eNB always transmits an RRC (Radio Resource Control) message.
In contrast to this, “Inter-eNB CA”, has been studied such that radio base stations eNBs can transmit their respective RRC messages as illustrated in a part (b) of FIG. 6 (For example, see Non-patent document 1).
For example, each radio base station eNB is expected to directly send a mobile station UE an RRC message for setting or changing the configuration specific to the radio base station eNB (the configuration is, for example, PUCCH (Physical Uplink Control Channel) resource, SRS (Sounding Reference Symbol) resource, or the like). Accordingly, it is expected that there is a possibility that the mobile station UE will simultaneously receive different RRC messages from different radio base stations eNBs.